Hi
I was running a Routeros 7.8 om Vmware Esxi 7.8 machine running Openvpn and L2TP services. CPU usage getting very high and finally 100% after awhile. Management and Ovpn tasks consume all CPU time without any reason until I reboot the router. Increasing number of virtual CPUs didn't solve the issue. Finally I downgraded to Ver. 7.6 and it solved. It seems there is a bug on OpenVPN service in version 7.8.

Very buggy in VXLAN, openvpn and CPU usage

There is an Alpha version 7.10.39 out, which fixed the CPU utilization problem on 7.8.
In the meantime, stay on 7.7 if you have an OVPN server running.